There may be hundreds of types of pasta in the world, but when in Rome, there are only 18 dishes you really, truly need to eat. The recommendations here come from some of the world’s foremost Italian experts, chefs, and restauranteurs in Italy and abroad. Chefs Davide Lombardi and Valerio Chicchierini of Cento Gourmet dispense with the homespun cliches most Roman trattorias lean on; recommended by Francesco Panella, owner of Antica Pesa in Rome and Feroce Ristorante in Brooklyn